(1) Field of the Invention
The present invention relates to a rubber composition having good breaking properties, and excellent vibration insulating properties and wherein the temperature dependence of the hysteresis loss of which is small.
(2) Description of the Prior Art
Heretofore, there has been known butyl rubber as a rubber developing excellent vibration-insulating and -absorbing properties over the widest temperature range among the vibration insulating rubber materials.
However, butyl rubber is poor in the breaking properties and compression set required as the vibration insulating rubber material. In order to satisfy the above requirements, therefore, it is attempted to blend butyl rubber with a synthetic diene rubber including natural rubber, but there is no covulcanization property between them and hence the breaking and compression set are not satisfactorily improved. As a result, such a rubber blend is naturally limited in the application as a rubber vibration insulator.
Under these circumstances, in the rubber industry, natural rubber, a synthetic diene rubber or a blend of other rubber therewith is used as a rubber vibration insulator by adding various plasticizers to provide the vibration absorbing property. In this case, however, the compression set reduces when intending to meet the vibration absorbing property, so that it is presently difficult to simultaneously satisfy both the properties.
Furthermore, it has been proposed to improve the vibration insulating properties by blending the above rubber with a polymer having a relatively high glass transition temperature Tg. In this case, however, the temperature dependence of hysteresis loss is large and the low temperature properties are disadvantageous, or the hysteresis loss becomes lower at high temperature, so that such a blend is restricted to application over a narrower temperature range.
With the recent developments in the automobile industry, the target value for the vibration absorbing property required for the rubber vibration insulator becomes severer year by year. Particularly, in the automobile parts to be used over a wider temperature range, it is demanded to develop materials for a rubber vibration insulator which have a small temperature dependence of the hysteresis loss and excellent vibration insulating properties without deteriorating other properties.